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The dependence of the interfacial tension of a phosphatidylethanolamine (PE) monolayer on the pH of the aqueous solution has been studied. A theoretical equation is derived to describe this dependence. A simple model of the influence of pH on the phosphatidylethanolamine monolayer at the air/hydrophobic chains of PE is presented. The contributions of additive phosphatidylethanolamine forms (both interfacial tension values and molecular area values) depend on pH. The interfacial tension values and the molecular area values for PEH(+) and PEOH(-) forms of phosphatidylethanolamine were calculated. The assumed model was verified experimentally. The experimental results agreed with those derived from the theoretical equation in a whole range of pH values.

We have monitored the effect of ergosterol on electrical capacitance and electrical resistance of the phosphatidylcholine bilayer membranes using chronopotentiometry method. The chronopotentiometric characteristic of the bilayers depends on constant-current flow through the membranes. For low current values, no electroporation takes place and the membrane voltage rises exponentially to a constant value described by the Ohm's law. Based on these kinds of chronopotentiometric curves, a method of the membrane capacitance and the membrane resistance calculations is presented.

The interfacial tension of lipid membranes composed of phosphatidylcholine (lecithin, PC)-valine (Val), phosphatidylcholine-isoleucine (Ile), phosphatidylcholine-tyrosine (Tyr), and phosphatidylcholine-phenylalanine (Phe) has been studied. The membrane components formed 1:1 complexes. The interfacial tension measurements were used to determine the membrane surface concentration A (3)(-1), the membrane interfacial tension γ(3), and the stability constant K.

We measured the interfacial tension of lipid membranes composed of ceramide-cholesterol, ceramide-sphingomyelin, and sphingomyelin-cholesterol. The membrane components formed 1:1 complexes. Interfacial tension measurements were used to determine the membrane surface concentration A 3 −1 , the membrane interfacial tension γ3, and the stability constant K.

Electrochemical impedance spectroscopy was used for the study of two-component lipid membranes. Phosphatidylserine and ceramide were to be investigated because they play an important biochemical role in cell membranes. The research on biolipid interaction was focused on a quantitative description of processes that take part in a bilayer. Assumed models of interaction between amphiphilic molecules and the equilibria that take place there were described by mathematical equations for the studied system. The possibility of complex formation for a two-component system forming bilayers was assumed, which could explain the deviation from the additivity rule. The molecular area and the equilibrium constant of the complex were determined.

Electrochemical impedance spectroscopy was used for the study of two-component lipid membranes. Phosphatidylcholine and ceramide were to be investigated, since they play an important biochemical role in cell membranes. The research on biolipid interaction was focused on quantitative description of processes that take part in a bilayer. Assumed models of interaction between amphiphilic molecules and the equilibria that take place there were described by mathematical equations for the studied system. The possibility of complex formation for two-component system forming bilayers was assumed that could explain the deviation from additivity rule. Equilibria were described by mathematical equations that were further verified experimentally. The determined values of parameters (stability constant, molecular area of complex, capacitance and conductance of the lipid membranes formed from molecules and complexes) were used for calculation of model curves. The comparison of model curves and experimental points verified the assumed model.

Electrochemical impedance spectroscopy was used for the study of two-component lipid membranes. Phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were to be investigated, because of their presence in biological membranes. Capacitance values of pure components are 0.62 and 0.32 μF cm −2 , respectively. The 1:1 complex was formed during formation of the PC–PE lipid membrane. Formation of the complex can explain the deviation from the additivity rule. This equilibrium was described by mathematical equations and was further verified experimentally. Adequate equations let us calculate such parameters as: capacitance of the complex molecule, area occupied by the complex molecule as well as the stability constant of the complex.

Interfacial tension has been determined for phosphatidylcholine-cholesterol, phosphatidylcholine-phosphatidylethanolamine, and phosphatidylethanolamine-cholesterol membranes. Phosphatidylcholine (PC), phosphatidylethanolamine (PE), and cholesterol (Ch) were to be investigated, because of their presence in biological membranes. Interfacial tension values of pure components are 0.81×10−3 N/m, 1.67×10−3 N/m, and 2.36×10−3 N/m, respectively. The 1∶1 complexes were formed during formation of the PC-Ch, PC-PE, and PE-Ch lipid membranes. The following parameters describing the complexes were determined: A 3 −1 , the surface concentrations of the lipid membranes formed from these complexes; γ3, the interfacial tensions of such membranes and K, the stability constants of these complexes.

The effect of ergosterol on the electrochemical features of the phosphatidylcholine bilayer membrane was investigated by impedance spectroscopy. The experimental impedance values obtained in the presence of different amounts of ergosterol showed evidence of domain structures within the bilayer containing

The effect of the presence of valinomycin in lecithin membrane on its interfacial tension has been studied. The experiments have been carried out at various forming solution compositions and at various potassium ion concentrations in electrolyte solution. Potassium chloride was used as the electrolyte. A complex was formed between the valinomycin molecule and K + ion. The following parameters describing the complex were determined: K , the stability constant of the valinomycin–K + complex and B , partition coefficient. These values are equal to 3.52 × 10 5 m 3 mol −1 and 6.0, respectively.

The effect of alpha-tocopherol on the electrochemical features of the phosphatidylcholine membrane was investigated by impedance spectroscopy. Phosphatidylcholine and alpha-tocopherol were chosen for the study because they are present in biological membranes and they fulfill essential functions in living organisms. The experimental impedance values obtained in the presence of different amounts of alpha-tocopherol showed evidence of domain structures within the bilayer containing less than 0.048 molar fraction of alpha-tocopherol. Based on derived mathematical equations, the surface area of phospholipid/alpha-tocopherol domain was calculated; it amounts to 832 A(2). This value is consistent, taking into consideration ordering and condensation effects of alpha-tocopherol, with the acknowledged, well documented, stoichiometry of such a domain of 10:1. The result of the investigation is the proposal of a new method for the determination of the surface area and description of the stoichiometry of domains formed in any two-component system.

Electrochemical impedance spectroscopy was used for the study of two-component lipid membranes. Phosphatidylcholine (lecithin, PC) and cholesterol (Ch) were chosen for the study because they are present in biological membranes and they fulfil essential functions in lively organisms. The theory of equilibrium between components of the membranes has been developed in order to obtain the parameters describing the PC Ch complex. The equilibrium between the PC, Ch and PC Ch complex on the basis of derived equations was considered and forming the 1:1 complex was proved. The following parameters of the complex were determined: capacitance (C3), conductance ( R 3 − 1 ) , area occupied by complex molecule (A3) as well as stability constant of the complex (K).

The effect of the presence of gramicidin D in a lecithin membrane on its interfacial tension has been studied. The studies have been carried out at various forming solution compositions and at various potassium ion concentrations in the electrolyte solution. Potassium chloride was used as the electrolyte. The complex was formed between the gramicidin molecule and K + ion. The following parameters describing the complex were determined: the surface area occupied by GK + complex ( A GK + ), the interfacial tension of the GK + membrane complex ( γ GK + ), and the stability constant of the gramicidin–K + complex ( K ). These values are 156 A 2 , 1.89 mN m −1 and 0.033 m 3 mol −1 , respectively.

It has been investigated whether it is possible to induce selectivity to polymer membranes by modifying them with an alkylated crown ether derivative. Polypropylene (PP) membranes were hydrophilized with 2-hydroxymethyl [18]corona-6 palmitate solutions of concentrations ranging from 0 to 60 wt% in a 1,2-dichloroethane-hexane solvent system of 1:4 volume ratio. The investigations were carried out by a impedance measurement method using two electrolyte solutions: 0.1 mol · dm−3 NaCl and 0.1 mol · dm−3 KCl. Changes in transport properties of the studied membranes were evaluated as a function of hydrophilizing agent concentrations. Electric resistance of the studied membranes was found to decrease drastically in the 0–5 wt% 2-hydroxymethyl [18]corona-6 palmitate concentration range, and it proved to be constant at higher concentrations. Non-Debye capacitance of the membranes increased in the 0–5% concentration range, and was constant at higher concentrations. Polypropylene membranes hydrophilized with 2-hydro...

This paper reports measurements on the pH dependence of the electrical capacitance of lipid membranes formed by 1:1 phosphatidylcholine-phosphatidylserine mixtures. A theoretical model was developed to describe this dependence, in which the contributions of functional groups (as the active centers of adsorption of the hydrogen and hydroxide ions) to the overall membrane capacitance were assumed to be additive. The proposed model was verified experimentally using electrochemical impedance spectroscopy. The theoretical predictions agreed with the experimental results over the measured pH range. A minimum corresponding to the isoelectric point appeared in both the theoretical equation and the experimental data.

The pH dependence of the interfacial tension is an important factor in the behavior of sphingomyelin (SM) monolayers. We developed a theoretical model to describe this dependence in which the interfacial tension and molecular area contributions of each sphingomyelin form were additive and dependent on pH. The interfacial tension values and the molecular areas values for the SMH(+) and SMOH(-) forms of sphingomyelin were calculated and the proposed model was experimentally verified. The theoretical predictions agreed with the experimental results for pH values ranging from 2 to 12.

Monolayers of phosphatidylcholine, tyrosine, and phenylalanine and binary mixtures phosphatidylcholine–tyrosine or phosphatidylcholine–phenylalanine were investigated at the air/water interface. Phosphatidylcholine (lecithin, PC), tyrosine (Tyr), and phenylalanine (Phe) were used in the experiment. The surface tension values of pure and mixed monolayers were used to calculate π–A isotherms. The surface tension measurements were carried out at 22°C using an improved Teflon trough and a Nima 9000 tensiometer. The Teflon trough was filled with a subphase of triple-distilled water. Known amounts of lipid dissolved in 1-chloropropane were placed at the surface using a syringe. The interactions between lecithin and amino acid result in significant deviations from the additivity rule. An equilibrium theory to describe the behavior of monolayer components at the air/water interface was developed in order to obtain the stability constants of PC–Tyr as well as PC–Phe complexes. We considered the equilibrium between the individual components and the complex and established that lecithin and amino acid formed highly stable 1:1 complex.

The basic electrical parameters of bilayer lipid membranes are capacitance and resistance. This article describes the application of chronopotentiometry to the research of lipid bilayers. Membranes were made from egg yolk phosphatidylcholine. The chronopotentiometric characteristic of the membranes depends on the current value. For low current values, no electroporation takes place and the voltage rises exponentially to a constant value. Based on these kinds of chronopotentiometric curves, a method of the membrane capacitance and the membrane resistance calculations are presented.

This chapter concerns the equilibria of some biomolecules in bilayer lipid membranes. The presented research of biolipid interaction was concentrated on quantitative description of experiments that take part within the bilayer as well as on its surface. Assumed models of interaction between amphiphilic molecules, between transport proteins and monovalent cations and the equilibria that take place there as well as acid–base equilibria were described by mathematical equations for the systems studied. These theoretical models were verified experimentally using interfacial tension and electrochemical impedance spectroscopy techniques. For systems of two kinds of lipids, the possibility of a 1:1 complex formation was assumed what would explain the deviation from the additivity rule. Calculated values of parameters (equilibrium constants, molecular areas of complexes, interfacial tensions, capacitances and resistances of molecules and complexes) were used for calculation model curves. The comparison of model curves and experimental points verified assumed models. The complex formation between the gramicidin molecule and K + ion was investigated by the interfacial tension method. Electrochemical impedance spectroscopy was used for the study of gramicidin D dimerization and transport of monovalent cations across lipid bilayers by the dimers. Both experimental methods mentioned were used for the research ability of valinomycin to form a 1:1 potassium-ion complex on the lipid bilayer/electrolyte solution interface. Very simple methods were proposed to determine the parameters used to describe the gramicidin dimer and ionophore-K + complexes. It could be demonstrated that determined parameters values were of a similar order of magnitude to those obtained by other measuring techniques. The effect of pH of electrolyte solution on the bilayer lipid membrane built from different lipids was also determined. The obtained curves demonstrate the maximal interfacial tension values at the isoelectric point. A course of these curves was well characterized by the simplified description based on the Gibbs isotherm, but only in proximity of the isoelectric point. While, using the exact definition of surface excess within the Gibbs equation (taking into account volumes of adsorbed ions at the membrane surface) permits us to explain the run of experimental curves in the whole pH range. Also in this chapter the models derived to describe adsorption of the H + and OH − ions at lipid surfaces formed from phospholipids were proposed, which would reproduce changes in interfacial tension more correctly, particularly in the ranges distant from the isolelectric point. In models, contribution of the individual forms of lipid molecule to interfacial tension of the bilayer was assumed to be additive. This chapter concentrated especially on phospholipids because they are major fractions of lipids found in biological membranes: phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylserine (PS) were chosen. PC was the basic component of the formed bilayers because it has been widely examined and described in the literature, but also because it creates permanent monolayers and bilayers, of which one can easily build in the other components. Cholesterol, gramicidin and valinomycin were also studied since they play an important biochemical role in cell membranes. Cholesterol is an important factor in controlling physical properties of biological membranes and their functions. Gramicidin is a model of more complicated biological ionic channels. For this reason, many studies have been done using this simple channel-forming polypeptide. It has been reported that valinomycin acts as a selective carrier of K + ions in a variety of cell membranes as well as on liposomes and lipid bilayers. The interactions between membrane lipids are nowadays intensively developed. This results from the suitability of this research for understandings of phenomena proceeding in cellular membranes. However, there is still the lack of the quantitative description of the systems. It is required for a better understanding of the processes that take place in biological membranes with the aim of forming the artificial membrane that would very closely resemble the properties of the natural membrane. Therefore, the knowledge of molecular structure and organization of phospholipids is necessary. Data presented in this work, received from mathematical derivation and confirmed experimentally are of great importance for interpretation of phenomena occurring in lipid monolayers and bilayers. These results can help in a better understanding of biological membranes and in their biophysical studies. Simple and very interesting methods proposed in this chapter can be used with success for the determination of the equilibrium constant value of any 1:1 lipid–other lipid complex and any 1:1 ionophore–monovalent ion complex and for acid–base equilibria between any phospholipids and ions from electrolyte solution (H + and OH − ).

Interfacial tension has been determined for phosphatidylcholine–stearic acid and phosphatidylcholine–stearylamine membranes. Phosphatidylcholine, stearic acid and stearylamine were used in the experimental. The interfacial tension values of the pure components are 1.62 × 10− 3 N/m, − 1.54 × 10− 2 N/m and 4.40 × 10− 3 N/m (hypothetical values), respectively. The 1:1 complexes were formed during formation of phosphatidylcholine–stearic acid and phosphatidylcholine–stearylamine membranes. The following parameters describing the complexes were determined: the surface concentrations of the lipid membranes formed from these complexes, A3− 1, the interfacial tensions of such membranes, γ3 and the stability constants of these complexes, K.

The effect of the ion carrier valinomycin on the electrochemical features of the phosphatidylcholine membrane was investigated by electrochemical impedance spectroscopy. Phosphatidylcholine and valinomycin were chosen for the study because they fulfil essential functions in lively organisms. The experimental impedance values obtained in the presence of different amounts of carrier, studied with several potassium ion concentrations, were used for the research ability of valinomycin to form a 1:1 potassium ion complex on the lipid bilayer/electrolyte solution interface. Based on derived mathematical equations, the heterogeneous equilibrium constant (K (h)), association rate constant of the complex (k (R)) and dissociation rate constant of the complex (k (D)) were calculated. The result of the investigation is the proposal of a new method for the determination of the parameters used to describe the chemical reaction at the interface between a carrier molecule from the membrane and a monovalent ion from the aqueous phase.

Electrochemical impedance spectroscopy (EIS) was used to the study of gramicidin D (GD) dimerization and to transport of monovalent cations across lipid bilayers by the dimers. Phosphatidylcholine (PC) membranes were studied, unmodified and modified with very low GD concentrations in the presence of various potassium ion concentrations. A new method was proposed to determine the parameters used to describe the gramicidin dimer: gramicidin surface concentration ( c GG ), area occupied by individual channel ( A G ) and gramicidin dimerization equilibrium constant ( K GG ). It was shown that electrochemical impedance spectroscopy measurements of lipid bilayer membranes yielded the K GG and A G values of the same order of magnitude as other measurement techniques.

Capacity and electric resistance of lipid membranes composed of lecithin and cholesterol were determined. The components were chosen for the study because they were present in biological membranes. Capacitance of the lecithin and cholesterol membranes amounts to 0.38 and 0.61 microF/cm(2), and resistance to 1.44(10(4)and 2.12(10(6)Omega cm(2), respectively. A 1:1 complex appears as a result of lecithin-cholesterol membrane formation. Parameters of the membrane formed of the lecithin-cholesterol complex were determined: surface concentration (Gamma(3)), capacitance (C(3)), and conductance (R;(3)(-1), as well as the stability constant (K) of the complex. The mean values of those magnitudes are as follows: 4.265(10(-6)mol/m(2), 0.54 microF/cm(2), 1.381(10(-6)Omega(-1)cm(-2)and 3.748(10(7), respectively.

Bilayer lipid membranes composed of phosphatidylcholine and decanoic acid or phosphatidylcholine and decylamine were investigated using electrochemical impedance spectroscopy. Interaction between membrane components causes significant deviations from the additivity rule. Area, capacitance, and stability constant values for the complexes were calculated based on the model assuming 1:1 stoichiometry, and the model was validated by comparison of these values to experimental results. We established that phosphatidylcholine and decylamine form highly stable 1:1 complexes. In the case of decanoic acid-modified phosphatidylcholine membranes, complexes with stoichiometries other than 1:1 should be taken into consideration.

This paper describes the application of chronopotentiometry to lipid bilayer research. The experiments were performed on bilayer lipid membranes composed of phosphatidylcholine and cholesterol and formed using the painting technique. Chronopotentiometric (U = f(t)) measurements were used to determine the membrane capacitance, resistance, and breakdown voltage as well as pore conductance and diameter.